Metallic scrap decontamination process

ABSTRACT

In a process for decontaminating contaminated metallic scrap, an oxygen bearing hot gas stream is passed into the inlet end of a container and is discharged from an exit end of the same container. The decontaminated scrap is loaded in the container at the inlet end. Concurrently the scrap is (a) moved from the inlet end to the exit end, (b) mixed and agitated within the interior of the container, and (c) during the mixing and agitation contacted with the hot gas stream moving through the interior of the container. The contact of the scrap with the hot gas stream is under conditions essentially capable of inhibiting flaming. By virtue of the contact with the hot gas stream, heat from the hot gas stream is transferred to the scrap, which lowers the temperature of the hot gas stream while raising the temperature of the scrap. This heat transfer takes the scrap to a first temperature phase wherein contaminants such as organics are volatilized and/or cracked into volatiles which become dispensed and diluted in the gas stream. Further, water is converted into steam. The volatiles including the steam are rapidly removed from the container by virtue of their disbursement into the gas stream. Further transfer of heat to the scrap raises the scrap to a second temperature phase wherein contaminants which are not volatilable, but which are subject to oxidation below 1200° F., are oxidized by oxygen in the gas stream. The scrap is maintained within the second temperature phase for a time sufficient to ensure complete oxidation and then the scrap is discharged from the container.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of my application Ser. No.771,846 filed Feb. 25, 1977 now U.S. Pat. No. 4,264,060 entitled "METHODAND APPARATUS FOR TREATING METALLIC SCRAP IN THE RECOVERY OF METALTHEREFROM", the complete disclosure of which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

This application discloses a process whereby metallic scrap can bedecontaminated in a container by concurrently passing in the samedirection both the scrap and a hot gas through the containertransferring heat from the hot gas to the scrap.

In my application Ser. No. 771,846 now U.S. Pat. No. 4,264,060 Idescribed some of the known art methods for decontaminating scrap.Briefly, these can be broken down as follows. Certain processesdecontaminate scrap by passing the scrap through a rotary kiln whichalso contains within the interior of the kiln a burner which heats theinterior of the kiln. Utilizing this type of process, the scrap withinthe kiln is subjected to direct impingement of the flame on the surfaceof the scrap. This is considered disadvantageous because those portionsof the scrap which are subjected to the flame are heated beyond thatpoint necessary to burn the scrap and in fact are heated to a pointwhere oxidation or melting of the metallic scrap itself takes place.

In a different type of decontamination process the scrap is placed ineither trays or in piles within a furnace. The scrap is heatedindirectly by heating either the walls of the furnace or the gaseswithin the interior of the furnace. This method has the advantage overthe previously described method in that the surface of the scrap is notdirectly impinged upon by the flame; however, since the scrap is eitherlocated in a container or in a pile the scrap within the interior of thecontainer or a pile in effect can only be heated by heat conducted bythe scrap surrounding it. In order to heat the scrap within the interiorof the pile sufficient to decontaminate it, the scrap on the exterior ofthe pile is heated to a point above that necessary to decontaminate itwhich results in surface oxidation. This process in effect is analogousto baking a roast in an oven. Before the middle is done, the outside isbrowned.

In a third process the scrap is passed through a rotating kiln and a hotgas is passed countercurrent to the scrap. A representative example ofthis process is that described in U.S. Pat. No. 4,010,935. In thisprocess the scrap exiting the kiln is at its highest temperature and itis at this point that it is exposed to the maximum temperature gas. Atthe inlet end of the kiln the scrap is relatively cool such as atambient temperature, and the gas exiting the inlet end of the kiln iscooler than the gas passed into the kiln at the scrap exit end of thekiln because it has lost heat to the scrap. To decontaminate the scrapthe scrap must be raised to a temperature causing decomposition of thecontaminants. Further, it must be held there for a time sufficient toensure complete decomposition. Since the scrap exiting the kiln contactsthe hottest temperature gas just prior to exiting the kiln either one orthe other of the following takes place. If the scrap is only raised tothe oxidation temperature at the moment it exits the kiln, it will notbe held at this temperature for a period long enough to ensure completeoxidation of the contaminants. If the scrap obtains the proper oxidationtemperature some time prior to when it exits the kiln, than if itremains in the kiln for a time period sufficient to ensure completeoxidation, because it will be further contacted with high temperaturehot gas before it is discharged from the exit end of the kiln, it willbe heated to a temperature greater than the optimum decontaminationoxidation temperature and will be exposed to temperature which can causemetal oxidation.

Most of man's most useful metals are found on the earth in the form ofores. To convert these ores to the free metals energy must be expended.It is also possible to collect used metals such as scrap and recyclethem or re-refine them into new starting stock for man's consumerproducts. With certain metals, aluminum being a representative example,conversion from the ore to the pure metal requires a greater energyexpenditure than conversion of reprocessed or scrap metals back intobasic feed stocks. In view of the necessity for energy conservation thereprocessing of scrap and used metals has become of paramountimportance.

BRIEF SUMMARY OF THE INVENTION

In view of the importance of reprocessing metallic scrap and in view ofthe deficiencies of the prior art processes known for doing the same itis considered there exists a need for improved processes for recoveringthis scrap. In view of this need it is a broad object to provide such aprocess. This broad object includes providing a process which is capableof handling scrap of varying sizes and thicknesses, scrap contaminatedwith a variety of different contaminants and including scrapcontaminated with both inorganic and organic contaminants such as paintpigments and oils. It is an additional object to provide a process inwhich the scrap is not subjected to direct impingement of flame orabnormally long exposure to eccessively hot gases.

These objects and additional objects which will be apparent in theremainder of this specification are achieved by providing a process ofdecontaminating contaminated metallic scrap which includes moving thescrap through a container from the inlet end of the container to theexit end of the container and concurrently moving an oxygen bearing hotgas through the container in the same direction as the scrap. While inthe container the scrap is mixed and agitated which serves to (a) exposethe scrap to the hot gas and (b) additionally cause the scrap to impingeupon itself flaking off contaminants adhering to the surface of thescrap. Small particle contaminants and/or fines within the scrap arepneumatically conveyed from the surface of the scrap by the hot gasstream. The hot gas stream transfers heat to the scrap whileconcurrently decreasing in temperature. This heats the scrap through afirst temperature phase wherein low boiling or temperature sensitivedecontaminants are volatilized and/or decomposed and the scrap isfurther heated to a second temperature phase wherein high boilingcontaminants are decomposed and the oxygen in the hot gas streamoxidizes the remaining oxidizable contaminants still adhering to thescrap. The scrap is maintained in the second temperature phase for atime period sufficient to insure complete oxidation of any oxidizablecontaminant and then the scrap is discharged from the container.

BRIEF DESCRIPTION OF THE DRAWING

This invention will be better understood when taken in conjunction withthe drawing wherein:

FIG. 1 shows a diagrammatic representation of the process of theinvention; and

FIG. 2 is a diagrammatic representation of the temperature phases of theinvention.

The invention described in this specification and the drawing utilizesand employs certain operative concepts and principles. These conceptsand principles are set forth and defined in the appended claims forminga part of this specification. Those skilled in the art to which thisinvention pertains will realize that these concepts and principles couldbe applied to a number of differently appearing embodiments. For thisreason the invention is not to be construed in light of only theembodiments described but is to be construed in light of the appendedclaims.

DETAILED DESCRIPTION

The process of the instant invention is carried out in a container 10having an inlet end 12 and an exit end 14. As shown in FIG. 1, at theinlet end 12 of container 10 contaminated metallic scrap not shown ornumbered is injected into the container 10 along with an oxygen bearinghot gas. The scrap is moved from the inlet end 12 to the exit end 14parallel within a hot gas flow and during this movement the scrap isalso moved within the interior space of the container such that it iscontinually mixed and agitated. This mixing and agitating exposes thescrap to the hot gas moving through the interior of the container andfurther, causes the pieces of the scrap to impinge or strike and scrapeagainst one another. After the process is complete the scrap isdischarged from the exit end of the container and the exhaust gas isalso discharged. When the scrap is discharged at the exit end 14 it hasbeen heated to a temperature sufficient to effect decontamination buthas not been overheated to the point wherein significant oxidation ormelting of the scrap itself has taken place. The exhaust gas exitingfrom the container 10 has been reduced in temperature to the pointwherein the exhaust gas and the decontaminated scrap are at or near thesame temperature.

The instant process is used to decontaminate metallic scrap which iscontaminated with a wide variety of different types of contaminants.This wide variety of contaminants would include cuttings or tailingsproduced during the machining or milling of parts and as such, this typeof scrap would chiefly be contaminated with oils and other lubricantsused during these machining or milling processes. Another source ofcontaminate scrap for the instant process would be scrap aluminum suchas aluminum cans and other aluminum containers used for the storage andtransporting of liquids and foods. This type of scrap will mainly becontaminated with paints, lacquers and organic litter. Depending uponthe prior processing of this type of scrap the scrap might also containlarge amounts of dirt and other small particles. Metallic scrap that ismainly of a ferrous nature can also be contaminated with oxides. Theinstant process includes physical abrasive contact between the scrappieces which helps decontaminate this type of contaminant.

When the scrap is loaded in the container 10 at the inlet end 12 it issubjected to forces causing three movements within the container 10. Thefirst movement is a general movement of the scrap from the inlet end 12to the exit end 14 of the container 10. This movement can be achieved bythe container 10 being set at an oblique angle or otherwise slopedcausing the scrap to generally descend from the elevated inlet end 12 tothe depressed exit end 14. Further, the container 10 can be fitted withinternal lifters or other devices which generally urge the scrap withinthe container 10 from the inlet end 12 to the exit end 14.

The second movement of the scrap within the container 10 is movementwithin the container transverse to the longitudinal movement of thescrap through the container 10. This transverse movement within thecontainer results in mixing and agitating of the scrap in localizedareas in the container 10. The mixing and agitating generally serve twodistinct purposes. The first is the scrap is continuously exposed to thehot gas moving along parallel with the scrap through the container 10.This contact with the hot gas causes transfer of heat from the hot gasto the scrap as hereinafter described. Secondly, the mixing andagitation of the scrap causes the scrap to impinge on itself. Thisimpingement results in the scrap acting as an abrasion agent on itself.This abrading action breaks loose both large and small pieces ofadhering contaminants such as paint flakes and/or rust spots. It furtherserves as a temperature modulator or normalizer in that the scrap bed iscontinually being agitated and the hotter pieces are continually beingre-oriented in respect to the cold pieces so that there is an effectiveheat transfer from the hotter pieces of scrap to the colder pieces ofscrap.

The third movement within the container 10 is a pneumatic movement ofsmall particles by the gas stream within the container 10. Thispneumatic movement is expressed as both movement of small particles ofcontaminants and/or fines contaminating the scrap as well as affecting amovement of the smaller pieces of scrap at an accelerated rate comparedto larger pieces of scrap. Depending on the scrap and the contaminant onthe scrap, there will be a varying degree of small particle contaminantsin the scrap. If the scrap contains a large amount of dirt and othercontaminants adhering to its surface, these contaminants which aregenerally 100% inorganic and thus not subject to low temperaturedecomposition are conveyed out of the container by the moving gas streamas they are continuously exposed to the gas stream by the transversemovement of the scrap within the container 10. Depending upon the scrapbeing decontaminated and its ultimate use this removal of small sizeinorganic particles, i.e., approximately 100 micron or less in size, canresult in less dross or slag being produced when the scrap, exiting thecontainer 10, is melted in a melter.

The pneumatic action of the hot gas on the smaller pieces of scrap helpsachieve the temperature control of the instant process in that thesmaller pieces of scrap have a high surface area compared to largerpieces of scrap and thus tend to heat up more rapidly. Because thesesmaller rapidly heated pieces of scrap are pneumatically conveyed withinthe container 10, in addition to the movements previously described theytend to progress from the inlet end 12 to the exit end 14 at a fasterrate than the bulkier pieces which are not pneumatically conveyed. Thisresults in less overall exposure to these smaller pieces to the hot gasflowing through the container 10 which ultimately results in limitingthe oxidation on the surface of these small pieces of scrap. Further, ashereinafter explained in greater detail part of the heating processwithin the container 10 results in oxidation of certain of thecomponents of the contaminants. After these contaminants are oxidizedthey generally are converted into carbon dioxide-carbon monoxide whichare removed by the pneumatic conveying effect of the hot gas. A portionof the remaining inorganic particles are removed from the surface of thescrap as described above by the impinging abrasion processes which freethem from the surface of the scrap.

The instant process typically will entail decontamination of pieces ofscrap ranging from about 3/8 inch thickness to about 0.004 inches inthickness. The larger pieces of scrap typically might range betweenabout 12 inches by 12 inches square or 3/8 inch cubes and the smallerpieces typically will be small shavings or other tailings produced inprocesses such as milling or crushing of recycled cans. The largerpieces of scrap typically will remain inside the container 10 for alonger period of time than the smaller pieces. Normally residence timefor the scrap will be from about three minutes to about 20 minuteswithin the interior of the container 10. For more homogeneous mixturesof scrap typical residence time will be from about five minutes to about15 minutes. These residence times within the container 10 are dependentupon a variety of factors . . . including scrap size as discussed--theoverall density of the bulk of scrap within the container 10, i.e., therate of scrap fed into and out of the container 10, and the inlettemperature of the hot gas. Additionally, the metallic nature of thescrap will also affect residence time; that is, aluminum scrap will haveone set of parameters governing the extremes of its residence timewithin the container 10 and other metals will each have their own set ofparameters.

FIG. 2 shows a diagrammatic representation of the temperature of boththe scrap and the hot gas within the interior of the container 10. Byuse of the instant process the temperature of the scrap exiting theoutlet end 14 of the container 10 can be controlled such that its exittemperature falls within a very narrow range of temperature variation.The instant process subjects the scrap to a particular heating cyclewhich allows for decontamination of the scrap, yet does not subject thescrap to such excessive temperature which will significantly oxidizeand/or melt the scrap.

Overall, the scrap is first placed at the inlet end 12 of the container10 normally when it is at or about ambient temperature. The hot gasentering the inlet end 12 of the container 10 is generally from about1100° to about 2000° F., preferably from about 1250° to 1600° F.Proximal to the inlet end 12 of container 10 the scrap is rapidly raisedthrough a first temperature phase generally occurring when the scrap isbetween 200° and 750° F. During this first temperature phase any wateror other liquids adhering to the surface of the scrap are vaporized intosteam or the appropriate gas obtainable from such other liquids.Concurrent with this, easily volatilized or low decomposing contaminantsare also volatilized and/or decomposed into volatile gases. Cracking oflarge molecules can occur during this process to produce secondaryvolatile products. The gases produced by the volatilization ordecomposition of the contaminants are disbursed into the hot gas streamflowing around the scrap. The mixing and agitating as previouslydiscussed helps to insure rapid dilution and/or disbursement of thevolatilized or decomposed products thus produced in the gas stream.

After passing through the first temperature phase the hot gas continuesto transfer heat to the scrap further lowering the temperature of thehot gas and raising the temperature of the scrap. The scrap is heatedfrom the temperature of the first phase through an intermediate phaseuntil it reaches about 850° F. at which time it enters the second phase.Normally all vaporization and non-oxidative decomposition have beeneffected by the time the scrap has reached 750° F. As the scrap passesthrough the intermediate phase which is generally between 750° to 850°F., it continues to absorb heat. During both the first phase and theintermediate phase the transfer of heat from the hot gas to the scrap isvery rapid. This results in the hot gas and the scrap both rapidlyapproaching an equilibrium temperature.

When the scrap is about 850° to 900° F. it enters the second temperaturephase and oxidation of the non-volatile or non-decomposable componentsof the contaminants is normally the dominant reaction. This oxidation isfurther controlled by the composition of the hot gas stream ashereinafter described. Generally, the scrap will be contaminated withcontaminants which will be completely oxidizable below about 1200° F.While it is considered that during the second temperature phaseoxidation is the predominating reaction, depending on the contaminantson the scrap, in addition to the oxidation reaction, volatilization andother non-oxidative gasification of the high boiling resins, tars,pitches and other similar contaminants, can also take place during thesecond temperature phase. If this type of high boiling or thermallystable contaminant is volatilized or decomposed into a flammable gasduring the second temperature phase, the gas thus generated will beremoved in the same manner as similar gases generated during the firsttemperature phase.

Depending upon the exact contaminant which is being removed from thescrap, the scrap will be raised to a final temperature of from about850° F. to about 1200° F. in the second temperature phase. Preferablythis second temperature phase will fall in the range of from about 900°F. to about 1050° F. Once the temperature of the scrap has reached theappropriate second temperature phase the scrap is held at thistemperature for a time sufficient to achieve complete removal of thecontaminants which are subject to thermal decomposition and/oroxidation. The inlet temperature of the hot gas is chosen from the rangepreviously described such that during the second temperature phase boththe scrap and the hot gas approach about the same temperature. Thisallows for continuous exposure of the scrap to the hot gas to hold thescrap at the final decontamination temperature without subjecting thescrap to higher gas temperatures which would further heat the scrapbeyond the desired second temperature phase final temperature. Normallythe time to insure complete decontamination of the scrap will be fromabout two to about 18 minutes. Thus, of the total residence time notedabove the majority of this time is spent with the scrap held at itsfixed final temperature to insure complete decontamination, said fixedfinal temperature being sufficiently low to insure that neither excessoxidation of the metal itself nor melting of the metal occurs.

During its residence time in the container 10 the scrap is heated by acombination of radiation, convection, conduction from the gas flow andabsorption of a portion of the heat generated in the exothermicreactions associated with cracking and/or oxidation of the hydrocarboncontaminants. Because of the mixing and agitation going on within theinterior of the container 10 heat is transferred not only from the hotgas directly to the scrap but from the hotter pieces of the scrap to thecolder pieces of the scrap. By use of the process of the instantinvention, the total body of a heterogeneous scrap composed of anassortment of sizes is raised to a uniform temperature, a temperaturesufficient to cause decontamination of the scrap without overheating thescrap.

The heating of the scrap within the container 10 is an essentiallyflameless heating. This flameless heating is achieved by a combinationof dilution of flammable volatiles within the hot gas stream, selectionof temperature of the hot gas stream and control of the oxygen contentof the hot gas stream.

In order to inhibit flaming, the oxygen content of the hot gas streamentering the container 10 at the inlet 12 is maintained between aminimum of 2% and a maximum of 8%. In order to insure complete oxidationof the oxidizable contaminants, some oxygen must be present. However, iftoo great an oxygen level is present in the first temperature phase ofthe process when the majority of the normal flammable contaminants arebeing volatilized, this high oxygen content will promote and/orperpetuate flaming of these volatiles within the container. The process,therefore, supplies oxygen sufficient to insure complete oxidation inthe second temperature phase but not an oxygen content high enough tosupport general flaming within the container 10. The oxygen content ofthe hot gas is also related to the temperature of the hot gas. If thetemperature of the hot gas stream introduced into the inlet end 12 isabout or is greater than 1500° F. the maximum oxygen content in order tostay within the non-flaming limit is about 4% to 6%. If the temperatureof the hot gas being introduced at the inlet end 12 of the container 10is less than 1500° F. the oxygen content can be raised to about 6% to8%.

As the volatile components are volatilized or decomposed in the firsttemperature phase they are transferred from the surface of the scrap tothe gaseous atmosphere inside the container 10. The flow rate of the hotgas through the container 10 is adjusted such that these volatilecomponents are diluted out into the hot gas stream such that incombination with the above described oxygen limits they are below theconcentration limit wherein flaming can be supported. Some verylocalized flaming may occur right on the surface of some scrap; however,this flaming cannot be perpetuated because the products that supportthis flaming are rapidly diluted below their flammability limit in thecontrolled atmosphere within the container 10 having the oxygen limitsas described and the temperature limits as described.

Normally the hot gas will flow through the container 10 from the inletend 12 to the exit end 14 at a velocity of from about 7 to about 12 feetper second. Mass flow associated with this velocity will result inlimiting the concentration of the flammable hydrocarbons per unit amountof gas flowing through the container. Generally this concentration willbe below the 25% flammability limit as established by existing fire codeguidelines. For furnaces with appropriate safety monitoring devices,this can be extended to a 50% limit. This limit can be expressed as theamount of Btu's of heat value of the flammable gas produced per pound ofhot gas in the container 10. Depending of course upon the particularhydrocarbon contaminant from which the flammable gas was derived,typically for the 25% limit the range will be from about 150 Btu's perpound to about 180 Btu's per pound with an average value of about 160Btu's per pound.

The hot gas which is used in the process can be generated specificallywithin the temperature and oxygen content level herein described, butpreferredly the hot gas will be gas produced as described in my abovenoted U.S. application Ser. No. 771,846. For use in assisting in mixingand agitating, the container 10 can be equipped with internal lifters orother equivalent mechanical components and the container 10 rotated toeffect the mixing and agitation.

The flow rate of the scrap through the container 10 will be governed bythe size and shape of its pieces in conjunction with the percentage ofand the type of contaminants contaminating the scrap. Typically, scrapcomposed mainly of cans will have contaminants in the order ofapproximately one to three percent by weight while mill turnings willhave contaminants in the order of about five to fifteen percent byweight. Since the mill scrap would produce more volatiles and flammablegases, its flow rate through the container 10 would be correspondinglyslower than an equal weight of can scrap and/or the flow rate of the hotgases for the mill turnings would be greater.

In order to insure maintaining the proper gaseous environment within theinterior of the container 10 in respect to both temperature and oxygencontent of the gaseous environment, the container 10 will generally besealed to the ingress of ambient gases into its interior.

I claim:
 1. A process for decontamination of contaminated metallic scrapwhich comprises:passing an oxygen bearing hot gas through the interiorof a container having an inlet end and an exit end, said hot gasentering said container at said inlet end and exiting said container atsaid exit end; locating said contaminated scrap within the interior ofsaid container at said inlet end; concurrently (a) moving said scrapfrom said inlet to said exit end of said container, (b) mixing andagitating said scrap within the interior of said container, and (c)contacting said scrap with said hot gas stream under conditionsessentially incapable of sustaining flaming within the interior of saidcontainer; said contacting said scrap with said hot gas transferringheat from said hot gas stream to said scrap lowering the temperature ofsaid hot gas stream, while concurrently raising the temperature of saidscrap (a) through a first temperature phase wherein low boilinghydrocarbons and water are volatilized and decomposed into gases whichare diffused into said hot gas stream and (b) to a second temperaturephase wherein high boiling contaminants are volatilized or decomposedand other contaminants which are essentially capable of being oxidizedbelow 1200° F. but which are not volatilized, are oxidized and (c)maintaining said scrap within the second temperature phase for a timeperiod sufficient to insure complete removal of said contaminants;discharging said decontaminated scrap from said container.
 2. Theprocess of claim 1 wherein:said first temperature phase is from about200° F. to about 750° F.
 3. The process of claim 2 wherein:said secondtemperature phase is from about 850° F. to about 1200° F.
 4. The procesof claim 3 wherein:said second temperature phase is from about 900° F.to about 1050° F.
 5. The process of claim 4 wherein:said hot gas streamis introduced into said inlet end of said closed container at atemperature of from about 1100° F. to about 2000° F.
 6. The process ofclaim 5 wherein:said hot gas stream is introduced into said inlet end ofsaid closed container at a temperature of from about 1250° F. to about1600° F.
 7. The process of claim 6 wherein:the temperature at which saidscrap is maintained within said second temperature range is from about900° F. to about 1050° F.
 8. The process of claim 7 wherein:saidconditions essentially incapable of sustaining combustion includecontrol of the temperature of said hot gas stream and control of theconcentration of said gasified hydrocarbons in said hot gas stream. 9.The process of claim 8 wherein:said conditions essentially incapable ofsustaining combustion include control of the temperature of said hot gasstream, control of the oxygen content of said hot gas stream, andcontrol of the concentration of said gasified hydrocarbons in said hotgas stream.
 10. The process of claim 9 wherein:the velocity of said hotgas stream passing from said inlet end to said exit end of saidcontainer is sufficient to suspend and maintain suspended within the hotgas stream a substantial portion of the unwanted fines and dustcomponents of said contaminants.
 11. The process of claim 8 wherein:saidvelocity is from about 7 to about 12 ft/sec.
 12. The process of claim 8wherein:said scrap is maintained in said container for a total residencetime of from about three minutes to about 20 minutes.
 13. The process ofclaim 12 wherein:said scrap is maintained in said container for a totalresidence time of from about 5 minutes to about 15 minutes.
 14. Theprocess of claim 13 wherein:said time period to insure essentiallycomplete oxidation is from about 2 minutes to about 18 minutes.
 15. Theprocess of claim 9 wherein:said oxygen content is less than about 8% andgreater than about 2%.
 16. The process of claim 9 wherein:saidtemperature of said hot gas stream is equal to or greater than 1500° F.and said oxygen content of said gas stream is less than 6% and greaterthan 2%.
 17. The process of claim 9 wherein:said temperature of said hotgas stream is less than 1500° F. and said oxygen content of said gasstream is less than 8% and greater than 2%.
 18. The process of claim 8wherein:flammable gases produced by volatilization are disbursed intosaid hot gas stream such that for each pound of said hot gas theconcentration of said flammable gases is below a concentration whichwill supply 180 Btu's of heat value from said flammable gas per pound ofhot gas.